This invention relates to centrifugal pumps generally, and more particularly to impellers for centrifugal pumps.
An impeller is a rotating component of a centrifugal pump which transfers energy from the power source that drives the pump to the fluid being pumped by accelerating the fluid outward from the center of rotation. The velocity of the impeller translates into pressure when the output movement is confined by the pump casing. Typically, an impeller includes a central hub or eye which is positioned at the pump inlet, and a plurality of vanes to propel the fluid radically. The central hub typically includes an axial bore or opening which may be splined to accept a splined driveshaft.
One of the major challenges of centrifugal pump design is dealing with axial loads. Generally, due to a large cross-sectional area of the impeller, a relatively small pressure differential across the impeller can translate into high axial loads on the pump's thrust bearing. The high axial loads can cause premature pump failure and frequent component replacement. As a result, large and expensive thrust bearings may be employed to handle the axial loads.
Several methods have been tried to reduce the effects of axial loading. These include the use of impellers with front and rear shrouds to fully enclose the impeller vanes, and of double-sided impellers. However, these impeller types do not typically provide a mechanism to counterbalance plug load—the hydraulic pressure load from the pump inlet, or other axial loads that are applied to the pump driveshaft.
Other methods for reducing axial loading include use of impellers with back pump-out vanes and impellers with labyrinth seals. However, these types of impellers are very sensitive to axial clearances. A slight change in axial clearance may significantly upset the axial force balance of an impeller with back pump-out vanes. Impellers with labyrinth seals can see significantly degraded performance due to high leakage variation caused by small changes in axial clearance. Reducing the sensitivity of these impellers to axial clearance may involve costly and complex design changes that increase the weight and reduce the reliability of the pump.
It would therefore be desirable to have a centrifugal pump impeller that effectively balances axial loads including plug loads, is not significantly affected by changes in axial clearance, and which does not require costly or complex design features that increase the weight and reduce the reliability of the pump.
Embodiments of the invention provide such an impeller. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.